Genesis of chrysoberyl in the pegmatites of southern Kerala, India

AbstractIn southern Kerala, India, chrysoberyl occurs in granitic pegmatites in association with quartz in alkali feldspar and is thought to crystallize earlier than beryl and sillimanite. The pegmatites are thought to have derived from the residual melts of granitic liquids formed by partial melting of the khondalites. In the absence of pyrometasomatic, desilication or aluminium-contamination processes, the genesis of chrysoberyl is explained by the CO2 activity in residual melts. This model is at variance with the known concepts and may also explain the genesis of chrysoberyl in Sri Lanka where it is still controversial.

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Geodynamic evolution of the southern Abitibi and Pontiac terranes: evidence from geochemistry of granitoid magma series (2700–2630 Ma)

Canadian Journal of Earth Sciences ◽

10.1139/e92-178 ◽

1992 ◽

Vol 29 (10) ◽

pp. 2266-2286 ◽

Cited By ~ 34

Author(s):

Rui Feng ◽

Rob Kerrich

Keyword(s):

Rare Earth ◽

Partial Melting ◽

Alkali Feldspar ◽

Quartz Syenite ◽

Southern Volcanic Zone ◽

Suprasubduction Zone ◽

Depleted Mantle ◽

Quartz Monzonite ◽

Ree Patterns ◽

Low K

Four distinct granitic series developed during the evolution of the Archean Abitibi Southern Volcanic Zone (SVZ): (1) A minor synvolcanic tonalite–trondhjemite–granodiorite (TTG) series was emplaced at ~2700 Ma, which has extremely low K2O (<1.5 wt.%), Rb (<50 ppm), and Sr (<200 ppm), higher Nb, Y, and Sc, flat rare-earth-element (REE) patterns, and negative Eu anomalies. (2) A voluminous tonalite – granodiorite – granite – quartz monzonite (TGGM) series developed syntectonically at ~2695–2685 Ma, and displays low K2O (1–3 wt.%), Rb (10–50 ppm), Ba (<1000 ppm), and U, enhanced Sr, depletion of Ta, Nb, and Ti, and strongly fractionated REE patterns (La/Ybn = 49–21). (3) A late-tectonic quartz syenite – quartz monzonite – granite (SMG) series was emplaced from ~2685 to 2675 Ma, and is grossly similar to the TGGM but has lower CaO/(K2O + Na2O) and greater concentrations of Rb, Ba, Th, and U. (4) A late-tectonic to posttectonic alkali feldspar syenite – alkali feldspar quartz syenite (SS) series was emplaced from 2680 to 2670 Ma, and occurs along regional strike-slip structures. The primitive rocks (SiO2 ≤ 65 wt.%) exhibit coenrichment of large-ion lithophile elements (LILE) and mafic elements (Cr, Co, and Ni) and strongly fractionated REE patterns, whereas evolved phases (SiO2 ≥ 65 wt.%) display lower contents of compatible and incompatible elements stemming from differentiation.In the adjacent Pontiac Subprovince and the Lacorne block within the SVZ, two granitic series predominate: (1) A syntectonic to late-tectonic monzodiorite–monzonite–granodiorite–syenite (MMGS) series (2690–2670 Ma) is comparable to the Abitibi SMG and SS series in most major-element, LILE, and REE contents but is distinguished by high MgO contents, extremely high Ba/Th ratios, and coenrichment of Cr, Co, and Ni with light rare-earth elements (LREE), Li, and Cs. (2) A garnet–muscovite–granite (GMG) series (2644 ± 13 Ma) displays K2O/Na2O ≥ 1, restricted SiO2 range (69–75 wt.%), pronounced enrichments of Rb, Li, Cs, Ta, Nb, Th, and U, and moderately fractionated REE's (La/Ybn = 16–0.9), with prominent negative Eu anomalies.The synvolcanic TTG series is interpreted to have formed by differentiation of low-K mafic magmas of the Blake River Group type in suprasubduction-zone environments. Geochemical compositions of the TGGM, SGM, SS, and MMGS series resemble those of Phanerozoic granitoids in island-arc settings and reflect a transition from partial melting of the subducted or subcreted slab to melting of the metasomatized depleted mantle wedge assisted by LILE- and LREE-enriched fluids released from the slab. The GMG, which formed by partial melting of the Pontiac metasediments when the Pontiac Sub-province collided with and underthrust the Abitibi SVZ at ~2670 Ma, is similar to Himalayan collisional leucogranites.

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The Cluanie granodiorite, NW Highlands of Scotland: a late Caledonian pluton of trondhjemitic affinity

Scottish Journal of Geology ◽

10.1144/0036-9276/01-373 ◽

2009 ◽

Vol 45 (2) ◽

pp. 117-130 ◽

Cited By ~ 1

Author(s):

I. Neill ◽

W. E. Stephens

Keyword(s):

Low Temperature ◽

Partial Melting ◽

Alkali Feldspar ◽

Field Investigation ◽

Strike Slip ◽

Fault System ◽

Scottish Highlands ◽

Dextral Shear ◽

Melting Experiments ◽

Xrf Analyses

SynopsisThe Cluanie Pluton is a late Caledonian granitoid emplaced into the Glenfinnan Division of the Moine Supergroup in the NW Scottish Highlands. A field investigation of the pluton and its internal facies is presented along with new major- and trace-element whole-rock XRF analyses, and geobarometric and geothermometric studies. Cluanie is predominantly composed of hornblende granodiorite characterized by varying concentrations of distinctive alkali feldspar megacrysts, with minor amounts of biotite granodiorite and rare mingled porphyritic microgranodiorite. The alkali feldspar megacrysts appear to be magmatic in origin. Rare spectacular pegmatitic concentrations most likely represent physical accumulation of the megacrysts. The pluton is geochemically a high Na/K trondhjemite, the only such pluton known among the Newer Granites of Scotland. On the basis of geochemical evidence and a comparison with partial melting experiments, we propose that the magmas were derived by fluid-rich melting of an amphibolitic source leading to relatively low temperature magmas which were significantly contaminated by Moine metasediments. The pluton was emplaced in the mid crust at about 4.3 kbar during an episode of dextral shear on the Glen Glass Fault related to regional strike-slip faulting on the Great Glen Fault system at c. 425 Ma.

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Granitic pegmatites in Sri Lanka: A concise review leading to insights and predictions

Ore and Energy Resource Geology ◽

10.1016/j.oreoa.2020.100011 ◽

2021 ◽

Vol 6 ◽

pp. 100011

Author(s):

P.L. Dharmapriya ◽

D.W.M. Disanayaka ◽

Robert F. Martin ◽

H.M.T.G.A. Pitawala ◽

Sanjeewa P.K. Malaviarachchi

Keyword(s):

Sri Lanka ◽

Granitic Pegmatites ◽

Concise Review

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C-type magmas: igneous charnockites and their extrusive equivalents

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s0263593300007847 ◽

1992 ◽

Vol 83 (1-2) ◽

pp. 155-164 ◽

Cited By ~ 76

Author(s):

Jonathan A. Kilpatrick ◽

David J. Ellis

Keyword(s):

Partial Melting ◽

Volcanic Rocks ◽

Alkali Feldspar ◽

Magma Type ◽

Mineral Assemblages ◽

Melting Event ◽

Distinctive Type ◽

High Concentrations ◽

Very High ◽

Inverted Pigeonite

ABSTRACTIgneous charnockites are characterised by distinctively high abundances of K2O, TiO2, P2O5 and LIL elements and low CaO at a given SiO2 level compared to metamorphic charnockites, and I-, S- and A-type granites. They form a distinctive type of intrusive igneous rocks, the Charnockite Magma Type (CMT or C-type), which generally lack hornblende and consist of pyroxene, alkali feldspar, plagioclase, quartz, biotite, apatite, ilmenite and titanomagnetite. Although this mineral assemblage superficially resembles that of metamorphic charnockites, magmatic charnockites are characterised by inverted pigeonite, exceptionally calcic alkali feldspar, potassic plagioclase, and coexisting opaque oxides, all with crystallisation temperatures of 950-1050°C. Apatite is a ubiquitous phase which, together with the very high concentrations of Zr and TiO2 over a wide silica range, is consistent with the derivation of the Charnockite Magma Type by very high temperature partial melting and fractionation.The credibility of intrusive charnockites as a magmatic type has historically foundered because of their apparent restriction to granulite belts and the absence of any reported extrusive equivalents. We report examples of volcanic rocks, of various ages, with the same distinctive major and trace element compositions, mineral assemblages and high temperatures of crystallisation as intrusive chamockites.The Charnockite Magma Type is considered to be derived by melting of a hornblende-free or poor, LILE-enriched fertile granulite source which had not been geochemically depleted by a previous partial melting event but which was dehydrated in an earlier metamorphism. Whereas H2O-saturated melting produces migmatites or "failed" granites, and vapour-absent melting of an amphibolite can produce I-type granites, according to this model the vapour-absent melting of a hornblende-free or hornblende-poor granulite at even higher temperatures produces charnockites.

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Derivation of A1-type granites by partial melting of newly underplated rocks related with the Tarim mantle plume

Geological Magazine ◽

10.1017/s0016756817000838 ◽

2017 ◽

Vol 156 (3) ◽

pp. 409-429 ◽

Cited By ~ 4

Author(s):

YUPING SU ◽

JIANPING ZHENG ◽

LILI LIANG ◽

HONGKUN DAI ◽

JUNHONG ZHAO ◽

...

Keyword(s):

Partial Melting ◽

Tectonic Setting ◽

Mafic Magma ◽

Alkali Feldspar ◽

Limited Range ◽

Granitic Rocks ◽

Large Igneous Province ◽

Mafic Rocks ◽

Mafic Intrusions ◽

Ultramafic Complex

AbstractThe granitic rocks of the Tarim large igneous province (LIP) are temporally and spatially related to mafic intrusions. However, their tectonic setting and genetic relationship are debated. Here, we report geochemical, and zircon U–Pb–Hf isotopic results for three alkali feldspar granitic plutons in the Halajun area, western margin of the Tarim Block. Zircon U–Pb ages suggest these plutons were emplaced at 268–275 Ma, coeval with the neighbouring mafic–ultramafic complexes and syenitic rocks. These granitic rocks have high contents of SiO2, alkalis, Rb, Th, Zr and REE (except Eu), and high ratios of FeO*/MgO and Ga/Al, and show strong depletions in Ba, Sr, Eu, which are commonly observed in the A1-type granites. Zircon Hf isotopes reveal a limited range ofεHf(t) values from −1.0 to +3.5 for different samples from three granitic plutons, obviously higher than those (mostly <0) of the mafic rocks. This distinct difference, along with a Daly gap and small volume of mafic rocks, argues against extreme fractionation of mafic magma as the main origin of the A1-type granites. Instead the A1-type granites were most likely derived from partial melting of newly underplated rocks triggered by the upwelling asthenosphere, followed by extensive fractionation. These A1-type granites were emplaced within an anorogenic setting during the late stage of the Tarim LIP, which possibly lasts for more than 30 Ma. The Piqiang mafic–ultramafic complex directly stemmed from asthenospheric mantle and Halajun A1-type granites represent two manners of vertical crustal growth.

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The granitic pegmatites of the Fregeneda area (Salamanca, Spain): characteristics and petrogenesis

Mineralogical Magazine ◽

10.1180/002646199548709 ◽

1999 ◽

Vol 63 (4) ◽

pp. 535-558 ◽

Cited By ~ 28

Author(s):

E. Roda Robles ◽

A. Pesquera Perez ◽

F. Velasco Roldan ◽

F. Fontan

Keyword(s):

Trace Element ◽

Partial Melting ◽

Fractional Crystallization ◽

Zonal Distribution ◽

Granitic Pegmatites ◽

Compositional Variations

AbstractPegmatites of the Fregeneda area, Salamanca, Spain, show a zonal distribution, from barren to enrichment in Li, Sn, Rb, Nb>Ta, B and P. They intrude pre-Ordovician metasediments which were metamorphosed to sillimanite-zone conditions near the Lumbrales granite. Field, mineralogical and petrographic data show the following zonal sequence from the granite outward: (1) barren pegmatites (pegmatites T1, T2, T3 and T4) with quartz, K-feldspar > albite, muscovite, tourmaline ± andalusite ± garnet; (2) intermediate pegmatites (types T5 and T6), characterized by the occurrence of beryl and Fe-Mn-Li phosphates; and (3) fertile pegmatites (dykes T7 and T8), with lepidolite, cassiterite, columbite, albite > K-feldspar, montebrasite and spodumene.Tourmaline from different pegmatites shows significant compositional variations. Trace element variations in mica and K-feldspar suggest that the origin of the different pegmatitic bodies may be explained by three different paths of fractional crystallization of melts generated by partial melting of quartzo-feldspathic rocks.

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Post-entrainment mineral–melt reactions in spinel peridotite xenoliths from Inver, Donegal, Ireland

Geological Magazine ◽

10.1017/s001675689700784x ◽

1997 ◽

Vol 134 (6) ◽

pp. 771-779 ◽

Cited By ~ 25

Author(s):

CLIFF S. J. SHAW ◽

ALAN D. EDGAR

Keyword(s):

Partial Melting ◽

Alkali Basalt ◽

Melt Inclusions ◽

Alkali Feldspar ◽

Spinel Peridotite ◽

Spinel Solid Solution ◽

Spinel Lherzolite ◽

Host Magma ◽

Chemical Signatures ◽

Na Depletion

Spinel lherzolite and harzburgite xenoliths hosted in an alkali basalt dyke near Inver, Donegal, Ireland show abundant evidence of interaction between xenolith minerals and the host melt. Of particular interest are primary Cr-diopside and spinel with sieve-textured coronas. Coronas on primary Cr-diopside are up to 3 mm wide and are associated with veinlets of devitrified glass. The coronas comprise secondary Cr-diopside with vermicular, interstitial alkali feldspar and chlorite grains up to 100 µm in size. The inclusion-free Cr-diopside cores are Al- and Na-rich whereas the coronas are Al- and Na-depleted and Ti-enriched. Sieve-textured spinels have similar texture to the clinopyroxene grains and are also associated with veinlets of infiltrated glass. However, the interstitial inclusions in the sieve-textured region are chlorite and nepheline. Inclusion-free spinel is part of a chromite–spinel solid solution and is Ti-poor. Spinel in the coronas has a greater chromite and ulvospinel component and falls close to a mixing line with spinel in the host alkali basalt. In addition to the sieve-textured grains, primary olivine in contact with infiltrated glass has Fe-rich rims, and orthopyroxene has broken down to form rims of olivine, clinopyroxene and a K-rich phase similar in composition to alkali-feldspar. Comparison of the compositions of the inclusion-free cores and sieve-textured rims shows that the rims have chemical signatures consistent with partial melting, that is, Al and Na depletion for clinopyroxene and Cr-enrichment for spinel. The textures of the coronas, particularly those around spinel and the reaction margins on orthopyroxene are identical to those produced during dissolution experiments.We suggest that silicate liquid from the host magma infiltrated the xenoliths during their ascent and since it was not in equilibrium with the xenolith minerals caused reaction. The occurrence of K-bearing interstitial minerals in the sieve-textured grains and reacted orthopyroxenes indicate that the coronas did not form by simple melting since none of the minerals that underwent breakdown are K-bearing. We suggest that the sieve-textured grains formed initially by partial melting and reaction associated with decompression and infiltration of liquid from the host magma. The melts included in the reacted phases were enriched in K by diffusion from the Si-poor infiltrated melt into the more Si-rich melt inclusions in the coronas.

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